Liquid crystal display device with protection circuit for electrostatic break down

Abstract

A liquid crystal display device has an insulating first substrate, a plurality of pixels, a plurality of image signal lines, a plurality of scanning signal lines, first and second common wirings disposed on the first substrate outside the display area constituted by a plurality of the pixels, a first electrostatic protection circuit disposed between the first common wiring and the scanning signal line for causing static electricity occurring in the scanning signal line, a second electrostatic protection circuit disposed between the second common wiring and the image signal line for causing static electricity occurring in the image signal line to flow through the second common wiring, a transparent second substrate opposing the surface of the first substrate on which the first and second common wirings are disposed, through a liquid crystal layer, and a conductor disposed between the first and second substrates for electrically connecting electrodes disposed on the second substrate to terminals disposed on the first substrate, wherein the first and second common wirings are electrically connected by a conductor member made of the same material as that of the conductor.

What is claimed is: 
     
       1. A liquid crystal display device comprising: an insulating first substrate;   a plurality of pixels disposed on said-first substrate and comprising a pixel electrode and a thin film transistor for selecting said pixel electrode;   a plurality of image signal lines for supplying an image signal to the thin film transistor of a corresponding one of said pixels;   a plurality of scanning signal lines for supplying a selection signal to said thin film transistor of said corresponding one of said pixels;   first and second common wirings disposed on said first substrate outside the display area constituted by a plurality of said pixels;   a first electrostatic protection circuit, disposed between said first common wiring and said scanning signal lines, for causing static electricity occurring in said scanning signal line to flow through said first common wiring;   a second electrostatic protection circuit, disposed between said second common wiring and said image signal line, for causing static electricity occurring in said image signal line to flow through said second common wiring;   a transparent second substrate opposing the surface of said first substrate on which said first and second common wirings are disposed through a liquid crystal layer; and   a conductor, disposed between said first and second substrates, for electrically connecting electrodes disposed on said second substrate to terminals disposed on said first substrate;   wherein said first and second common wirings are electrically connected by a conductor member made of the same material as that of said conductor.   
     
     
       2. A liquid crystal display device according to claim 1, wherein each of said first and second electrostatic protection circuits is constituted by connecting a diode in the forward direction and a diode in the reverse direction in parallel with each other. 
     
     
       3. A liquid crystal display device according to claim 2, wherein each of said diode in the forward direction and said diode in the reverse direction is formed by using a MIS transistor and connecting the gate electrode of said MIS transistor to its source electrode. 
     
     
       4. A liquid crystal display device according to claim 3, wherein said MIS transistor is formed simultaneously with said thin film transistor.